1. Field of the Invention
The present invention relates to a water-based ink set for ink-jet recording suitable for reducing graininess in a low density printed part, for extending a color reproduction range, and for preventing blurring and color unevenness in a portion recorded with red, blue or green ink. The present invention also relates to an ink-jet recording method using this water-based ink set for ink-jet recording.
2. Description of the Related Art
When a color image is developed by use of an ink-jet recording method, a three-color ink set has been generally used which is composed of a yellow ink (Y), a magenta ink (M) and a cyan ink (C). Moreover, a four-color ink set has also been used in which a black ink (K) is further added to the three-color ink set.
Generally, in an ink-jet recording method, the gradation of an image is controlled by adjusting the density of dots formed by ejecting ink onto a recording material. However, when the gradation is controlled by such a method, the dot density decreases in a low density printed part. Relative to this, the individual dots become easily discernable to the eye, thereby causing a problem that the image is grainy.
In view of the above, a method has been proposed in which two or more inks are employed as cyan ink (Japanese Patent Application Laid-Open No. H01-95093). In this method, these inks have different dye concentrations and are composed of different kinds of dyes. In addition, a dye which is excellent in vividness but inferior in light fastness is employed in a dark color ink, and a dye which is excellent in light fastness but inferior in vividness is employed in a light color ink. Moreover, a similar method has been proposed for magenta ink (Japanese Patent Application Laid-Open No. H02-127482). According to these methods, graininess can be improved, but a problem remains that a color reproduction range cannot be extended.
Generally, in a three-color ink set composed of yellow, magenta and cyan inks, and also in a four-color ink set in which a black ink is added to the three-color ink set, red color is developed by use of the magenta ink and the yellow ink. When these two inks are used to develop red color as above, problems arise due to a landing error of superposition. That is, sharp printing quality is difficult to achieve, and colors are difficult to be vividly developed. Similar problems arise when blue color is developed by use of the magenta ink and the cyan ink or when green color is developed by use of the cyan ink and the yellow ink.
Recently, color text printing has been increasingly employed. However, in this case, a problem arises that the edge of a line, which is ideally smooth and straight, becomes blurred in an extremely wavy manner in color text.
In order to improve the blurring, a method has been generally employed in which the penetrability of color ink is lowered. However, a recording material such as recording paper has a portion into which ink easily penetrates and a portion into which ink does not easily penetrate, depending on surface conditions such as the irregularity of the fiber constituting the recording material. If the penetrability of color ink is simply reduced, the non-uniformity of the ink penetrability of the recording material results in the variation of the ink penetration amount on a printed material. Thus, inconsistency in color density or color unevenness is likely to occur in a portion which is intended to be printed in a single color. On the other hand, when the ink penetrability is made to increase in order to improve the color unevenness, the color unevenness is improved, but blurring occurs in color text printing.